This invention concerns a novel alloy of which the constituents, or the principal constituents, are magnesium, zinc and aluminium, said alloy being particularly suitable for use in the production of, or incorporation into, products in the form of pellets containing magnesium and other metallic, animal-dietary supplements or active agents for administering to ruminants by deposition into the rumeno-reticular sac, for example by means of an oesophageal balling gun, where they dissolve in the rumen juices, e.g., over a period of several weeks, to provide a continuous or dosed supply of magnesium with or without other valuable metallic elements and/or active agents for assimilation by the animal. The invention further concerns products in the form of pellets as aforesaid.
The specification of British Patent No. 1 030 101 teaches that pellets for administration to ruminants should have a preferred minimum density of 2.25 gm/ml to avoid shedding by the animal, and proposes a suitable alloy containing at least 75% magnesium and having a preferred aluminium content of 8 to 15%. These percentages are by weight and wherever percentages are recited in this specification, they are all given by weight. The density of such alloys is approximately 1.8 gm/ml and to achieve a pellet with a density in excess of 2.25 gm/ml it is necessary to weight the pellet by incorporating a dense insoluble material, such as iron shot. A commercially-available pellet has heretofore been manufactured from a magnesium-based alloy containing 12% aluminium and 2% copper weighted by reason of approximately 50% of the overall weight of the pellet being of fine iron shot. Such pellets have a density of approximately 2.8 gm/ml and have been widely used for the protection of cattle and sheep from hypomagnesaemia.
The known pellets are difficult to manufacture due to the wide difference between the density of the magnesium alloy (1.8 gm/ml) and that of the iron (7.3 gm/ml). A usual method of fabrication utilises the wide freezing range of the magnesium alloy. The alloy is heated to an elevated temperature between its liquidus and solidus points and the required quantity of iron shot is mixed with the resultant pasty alloy. The pasty mixture, at the elevated temperature, is introduced into open mould cavities and pressed to the required shape. Difficulties are experienced with such manufacturing processes, arising from segregation of the iron shot and the aluminium-rich eutectic constituent of the magnesium alloy. It is also necessary to avoid alloying of the surfaces of the iron shot particles if the corrosion rate of the pellets is not to be adversely affected.